This invention relates to locks, for instance of the type known as cylinder locks, that is, locks which comprise a generally cylindrical body for attaching to a door or to a latch mechanism mounted on a door, the body containing a rotatable barrel which can be turned by means of an appropriate key inserted into a key slot in the barrel. The invention further relates to keys and to combinations of locks and keys.
Locks of this type are in very widespread use and in recent years there have been many attempts to replace locks of this type with electrically actuable locking means instead of the usual mechanically actuable locking mechanism which normally locks the barrel in position when the appropriate key is not in position in the key slot. The change to an electrically actuable locking means is intended to enable a very high level of security to be obtained by virtue of the very large number of key combinations which can be achieved utilising an electronic form of coding of the key.
Considerable effort has been expended on designing systems for reading various forms of code written on keys, often with a view to ensuring that keys which are used in the electrically actuable locks are also usable with other locks of the same basic type which are mechanically actuable.
One of the problems which arises, however, is the provision of a suitable source of operating power for the lock and electronic cylinder type locks currently in use require a battery to be installed to act as such power source. The result of this is that installation of an electronic cylinder type lock is made very complicated and it is certainly not possible to substitute an electronic cylinder lock for a conventional mechanical one without either cutting an enlarged rebate in the door to house the batteries or adding a special-purpose battery holder/bezel to the lock.
Preferred embodiments of the invention are defined in the other appended claims.
It is thus possible to provide an electronic cylinder-type lock which can be used as a direct replacement for a conventional mechanical cylinder-type lock.
To this end there may be provided a battery-less electronic cylinder-type lock in which means is provided for acquiring electrical power for the circuits contained in the lock from a battery contained in a coacting key.
Power transfer may be made by transformer coupling between a winding in the key and a winding in the lock, such coupling being established when the key is inserted into the key slot of the lock barrel. Circuits within the key apply alternating current to the winding in the key and the circuits in the lock include a rectifying circuit for rectifying alternating current induced in the winding in the lock. With such an arrangement the circuits in the key may be such as to modulate the alternating current signal applied to the key winding so as to transmit to the lock circuits signals representing a key code characteristic of the key.
Alternatively, power may be supplied to the lock circuits via a simple direct mechanical contact arrangement.
In either case, the circuits of the lock may be arranged (on receipt of an appropriate code from the key) to energise either a low energy electromagnet arrangement for unlocking the barrel, or a thermally operated actuator arrangement, such as a nickel-titanium wire actuator.
It is already known to transmit electrical power between a key and a lock and also to superimpose code signals to enable circuits in the lock to recognise a code characteristic of a key. However, with such arrangements, transfer of power is from a battery or other power source in the lock to circuits in the key to enable the key to transmit its coded signals.
The applicants have appreciated for the first time that the presence of a battery in an electronic lock is a severe disadvantage. As mentioned above, not only does the need for a lock battery confound or at least complicate installation of an electronic lock in place of a mechanical one, but failure of the battery will lead to very considerable problems. Access to the battery is usually only obtainable when the door controlled by the lock has been opened and it is therefore necessary for a battery-operated lock to have some means for actuating the lock in such an emergency situation. This will inevitably lead to considerable inconvenience for the user unless the emergency procedure is one which will very seriously compromise the security of the lock.
When the lock is battery-less, on the other hand, the failure of the battery in a key is not a serious matter and the door can still be opened by other keys. Battery replacement can be very simply carried out without comprising system security at all.
Electronically actuable locks are usually used only in situations where there are a several keys in regular use and whilst each lock may be operated with considerable frequency the frequency of use of each key will be comparatively low. It is therefore possible to attain an acceptably long battery life from a relatively small battery as compared with the type of battery needed for installation in the lock.